I agree with habdab that it is a true bug (Hemiptera), and most probably a shield bug (Pentatomidae)

However, hudl, when making comparisons with images on the internet, bear in mind that yours is not an adult. It looks to be a final instar (last nymph stage before adult). The appearance of true bugs changes considerably as they develop.

Nezara viridula (southern green shieldbug) is not far off, but certainly not identical - see

Notice how individuals, even of the same instar of the same species, can look very different - look at the last three photos on that page - they are all final instar nymphs. Yours may yet prove to be of this species.

There are plenty of other bugs listed on that (excellent) site, including these drawings

Mark Hardman, Yes the bug is still alive, it is in a jamjar with a leaf from some brocolli. It came with some blackberries from Tesco which were from Mexico. Maybe it has come from there? Yes I do live in Britain.

May I suggest that if you have a sprig of foliage in water, then cover the water with a layer of cotton wool to prevent the bug from accidently drowning. Not too sure how suicidal bugs are but I know Reptiles can drown easily in captivity.

Thanks for that, will put some greenery in wrapped in damp kitchen roll to help keep in fresh. What I'm going to do with this bug if it doesn't die I do not know, I certainly can't let it out as it may not be native.

If it survives, we stand a better chance of identifying it, and then we can decide (perhaps) if the authorities should be notified.

Precautions against bug drowing would do no harm, but in this sort of case -where there is a plant stem serving as a route out of the water- I think the risk is relatively small, especially if the stem is kept in touch with the inside of the vessel.